In a conventional biosensor, a reagent layer containing at least an oxidoreductase and an electron transfer mediator (also referred to as “mediator,” “electron transfer substance,” or “electron carrier”) is disposed on two or more electrodes formed on an insulation substrate.
In a biosensor of this type, exchange of electrons is performed between substance to be measured and oxidoreductase, and the electrons then move via the electron transfer mediator to the electrode, allowing the measurement of the current value.
Examples of the aforementioned biosensor include a biosensor in which a reagent layer containing glucose dehydrogenase as an enzyme and potassium ferricyanide as an electron carrier is formed on a counter electrode, a measurement electrode, and a detection electrode.
In this biosensor, the reagent layer is dissolved into blood having been sucked into a specimen supply path, and an enzyme reaction proceeds with glucose which is a substrate in the blood.
Then, the electron carrier is reduced, and thereby, a reduced-type electron carrier is formed. When the reduced-type electron carrier is electrochemically oxidized, this causes an electric current, and the glucose concentration in the blood is measured based on the value of the current thus obtained.